1. Field of the Invention
The present invention concerns improvements to hydraulic distributors.
2. Prior Art
By way of example, FIG. 1 of the attached drawings shows, in cross-section, a known embodiment of such a distributor as it appears in FIG. 1 of the document FR-A-2 689 575 in the name of the common assignee.
The distributor comprises a body 1 provided with an intake orifice P for pressurized fluid supplied by a hydraulic source (not shown). In the example illustrated, said orifice P has the form of a channel 2 passing transversely 1 through body 1 in the plane of the drawing and emerging on the two main faces of said body which serve as contact faces when several distributors are stacked side-by-side and one against the other. At least one orifice T (having the form of a channel passing transversely through the body 1 in the plane of the drawing and emerging on the two main faces of said body) serves to return the fluid to a tank (not shown). Two working orifices A, B are connectable to a hydraulic device or receiver (not shown). A distribution valve slide 4 is able to slide in a bore 5 passing longitudinally through body 1 and emerging on two opposed faces of the ends 6, 7 of the body. In the conventional manner, the body 1 and the valve slide 4 include passages and/or channels and/or grooves arranged to co-operate in order to establish and/or interrupt the connections between the different orifices P, A, B, T of the distributor body according to the axial position occupied by the valve slide in the bore. The specific arrangements of these passages and/or channels and/or grooves are determined by a person skilled in the art in relation to the desired functions of the distributor.
In addition, in this specific example, the body 1 also includes a further transverse channel 8 extending between the main faces of the body and combined with at least one pressure selector allowing to be transmitted, in a channel 18 situated downstream of the distributor valve slide 4, the higher (xe2x80x9cload sensingxe2x80x9d or LS pressure) of the two pressures constituted respectively by the pressure in said channel upstream of the distributor and a working pressure of the distributor.
The channel 2 connected to the intake orifice P emerges in the bore 5 of the body in an intake chamber 10 of said body, close to which another chamber 11 communicates, via a passage 12, with a housing 13 in which a plunger 14 is mounted freely sliding and forming a fluid-tight seal. Passage 12 emerges into housing 13 at one end of the latter, here the lower end (corresponding to one end face of plunger 14, here its lower end), while at its opposite end (here its upper end) housing 13 opens into a cavity 15 in which the head 16 of plunger 14 can move. Head 16, wider in relation to the body of the plunger, can rest on a shoulder formed at the opening of housing 13 into cavity 15 to retain the plunger 14. A spring 17 is provided in cavity 15 to press plunger 14 against said shoulder so as to fix its position in the absence of pressure. The above-mentioned channel 8 emerges in cavity 15 in such a way that the pressure prevailing in channel 8 is also present in cavity 15 and is therefore exerted on the corresponding end of plunger 14 (here its upper end).
In addition, plunger 14 includes an axial channel 18 emerging, on one side, in its end face opposite passage 12 and, on the other, in a diametrical channel 19 passing through plunger 14 and so arranged as to be closed by the wall of housing 13 when plunger 14 is in the rest position determined by spring 17 (shown in FIG. 1) or in a not fully raised position. A part 28 of axial channel 18 is formed as a restriction or nozzle.
The portion of valve slide 4 which extends, in the neutral position, between chambers 10 and 11, isolating them from each other, is provided with progressive notches 20 intended to ensure a controlled flow of hydraulic fluid in the appropriate direction when the valve slide is displaced in one direction of the other. Two conduits 21 extend from above-mentioned housing 13 in two approximately diametrically opposite directions, in one or both of which conduits a non-return valve 22 is arranged, the two conduits 21 emerging in two respective chambers 23 in bore 5.
In the proximity of chambers 23 two respective distribution chambers 24 of bore 5 are connected by conduits 25 to the respective working orifices or outlet orifices A and B of the distributor.
Finally, beyond distribution chambers 24, two return chambers 26 of bore 5 are connected respectively by conduits 27 to return channel 3 emerging into the return orifice T.
The operation of the distributor just described is explained in detail in document FR 2 689 575 already cited, to which reference may be made.
Although a distributor arranged as just described is satisfactory with regard to its general principle of construction, it nevertheless has a disadvantage in certain operating conditions. Such a distributor is intended not to be used alone but in association with several other distributors of the same type to form a multiple hydraulic distribution device. The distributors are then preferably stacked in a fluid-tight manner one against the other by their main or large faces so that the respective conduits P, T and LS (channels 8) all communicate with each other and form conduits passing from one side of the stack to the other to enable the assembly to operate as a multiple distribution device.
When, in such a multiple distribution device, several sections (single distributors) are actuated simultaneously for large movements of the hydraulic receivers supplied, instabilities due to the inadequate damping of the movements of the balances occur. In other words, because of the simultaneous movements of the balances in the respective distributors, the balances react on each other through the intermediary of channel LS and it is difficult to establish equilibrium in pressure LS.
The objective of the invention is therefore to provide an improved arrangement of the distributor which avoids this disadvantage and which leads to rapid stabilization of pressure LS in the case of multiple actuation.
To this end, a hydraulic distributor comprises a regulating balance able to perform a function of detecting the highest charge pressure, an anti-saturation function and a delivery-dividing function independent of the charge, this balance including a housing hollowed in the distributor body and in which a plunger is movable, this housing comprising:
a first end able to receive selectively the pressurized hydraulic fluid delivered by a hydraulic source,
a second end in communication with a channel conveying the highest charge pressure, and
a lateral orifice communicating selectively with a working orifice of the distributor, said plunger including a passage provided with a restriction and opening, on one side, towards said first end of the housing and, on the other, opening laterally so as to emerge in the above-mentioned second end of the housing when the plunger occupies a position determined by the excess of said intake pressure reduced by the pressure drop caused by the restriction, as compared to the highest charge pressure prevailing in the above-mentioned second end of the housing, said plunger being arranged to uncover the lateral orifice of the housing and to connect the latter with the first end of the housing in proportion to the pressure differential between the intake pressure and the highest charge pressure prevailing in the second end of the housing.
The hydraulic distributor, arranged in accordance with the invention, is characterized in that the balance comprises:
a fixed central core extending in the housing and coaxially with it;
the tubular plunger interposed sliding freely, coaxially, between the core and the housing, said plunger having a length less than that of the core and being so configured externally as to cover or uncover the lateral orifice more or less according to its position,
the core and the plunger being mutually configured to define between them an annular chamber having a first radially extending annular surface defined by the plunger,
a second radially extending annular surface located on the plunger and facing towards the first surface and being adapted to be subjected to the pressure of the intake fluid,
a central passage formed in the core and including a first orifice emerging in the above-mentioned second end of the housing in which the highest charge pressure prevails, a second orifice emerging in the above-mentioned annular chamber between the core and the plunger in such a way that the pressure is exerted on the annular surface of said chamber, and a third orifice located opposite the above-mentioned first end of the housing and being closed by the plunger as long as the charge pressure of the distributor does not constitute the highest charge pressure.
The balance arrangement which has just been described retains the basic provisions and functions of the balance used in the known distributor shown in FIG. 1. The fixed central core incorporates the nozzle of the linking conduit between the first end of the housing receiving the intake fluid and the second end of the housing under the pressure LS; the tubular plunger, sliding around the central core, permits the generation of the pressure differential xcex94p between the pressure of the fluid coming from the hydraulic source and the charge pressure delivered to the lateral orifice of the housing, then to the working orifice.
Furthermore, the second orifice of the core passage is preferably provided with a restriction so that movement of the plunger is restricted hydraulically: in this way damping means are provided (chamber with variable volume defined between the tubular plunger and the central core and connected to the central passage by said second nozzle) which control the movement of the tubular plunger and avoid vibration of the latter.
In an advantageous embodiment, the core includes a widened body in the area of the second end of the housing and a narrowed portion in the area of the first end of the housing; the tubular plunger includes a portion of large diameter surrounding the widened body of the core and a portion of small diameter surrounding the narrowed portion of the core; and the length of the widened body of the core is less than that of the large-diameter portion of the plunger so as to define the above-mentioned annular chamber between the core and the plunger.
Interestingly, the restriction of the balance is arranged in the third above-mentioned orifice of the core passage.
In an example of a structurally simple embodiment, the housing is formed by a bore opening on one face of the distributor body and this bore is closed by a fluid-tight plug which blocks the core in the housing.
Finally, to reduce machining of the parts as much as possible the central core can be made of unfinished cast iron or bronze and the tubular plunger can be of steel which is precision-finished on its inner face.